1. Field of the Invention:
The invention is directed towards a system of non-contact detection of acoustic airborne noise caused by water or steam leaks in boilers, etc.
2. Description of the Prior Art:
Steam or water leaks in recovery boilers are dangerous. In other types of boilers such as fossil fuel boilers, the leaks may not be dangerous, but may be expensive to fix if not detected early. Generally, two methods of detection have been developed, one based on detection of airborne sounds by suitable microphones, and the other based on the detection of ultrasonic waves by piezoelectric transducers in contact with the walls of pipes carrying water. Microphones are delicate and suffer from corrosion problems in the harsh environments of such boilers even when provided with cooling.
Diaphragmless microphones with carbon granules as the sensing element have been proposed by the applicant as a low cost, rugged device for use in harsh environments as described in the U.S. Pat. NO. 4,498,333. However, an even more promising device, the laser Schlieren microphone, can be produced to satisfy the need for a sensor that detects the sounds of leaks.
U.S. Pat. Nos. 3,028,450 to Manning, 3,168,824 to Florer, et al., 3,209,344 to Miller, 3,831,561 to Yamamato, et al. and 4,309,576 to Corrigan disclose detection systems for water or gas leaks. The patent to Yamamato is specifically directed to detection of leaks in recovery boilers. None of these patents discloses or suggests the use of a laser Schlieren microphone.